1. Field of the Invention
The present invention relates generally to a solar water heating device, and more particularly to a compound solar water heating and dehumidifying device which may slow down dissipation of heat from a water tank and which has the functions of a dehumidifier.
2. Description of the Prior Art
Solar water heating systems generally fall into three main types, namely, the natural circulation type, the forced circulation type, and the storage type. In the natural circulation type, a working fluid, i.e., water, is caused to circulate between a water tank and water channels of a plate type heat collector by utilizing the siphon phenomenon, without requiring a motor to pump the water. In this system, cold water in the water channels on the heat collector absorb the sun's radiant heat on the plate surfaces so that the temperature of the water rises while the density thereof drops. Hence, hot water rises up to the water tank via a water conduit. This is the so-called siphon phenomenon.
At the same time, the water that is originally stored in the water tank and has a lower temperature and density will flow downwardly to the water channels on the heat collector to be subject to the sun's heat and undergo heat transfer. The siphon action is therefore repeated to cause water stored in the water tank to be heated and circulated in natural cycles.
In the above-described natural circulation type of solar water heaters, a certain volume of water continuously absorbs solar energy in the day-time via the heat collector, and the heated water is caused to flow upwardly to the water tank by siphon action. But with the continuous rise of the temperature of water inside the water tank, the siphon effect will slow down. Besides, heat loss will increase due to augmentation of the temperature difference between the heat collector and the ambient air. Therefore, at noon time when sunlight is most intense, the heat collecting efficiency and the rise of water temperature will tend to slow down. In the afternoon when sunlight becomes less intense, it is possible that the heat collecting efficiency will drop rather than rise, and the temperature of water in the water tank will no longer climb. Instead, the water temperature will fall as a result of the drop in heat collecting efficiency. This problem is especially obvious when sunlight is not stable, or on overcast days, or at night.
In view of the above, it can be seen that, with the conventional plate type solar heater, the heat accumulation capacity of the water tank is quite restricted even when the sky is clear and sunlight is normal. In sum, as the temperature of hot water in the water tank will rise to its peak when the sun's light is most intense but will drop when the sun's light becomes less intense, and as the temperature difference between water in the tank and the ambient air leads to heat dissipation, conventional solar water heaters cannot effectively utilize solar energy for at least one third of the day even when sunlight is normal. In particular, at night time when the temperature difference between water in the tank and the ambient air becomes greater and there is the radiant heat effect, the heat collector will become a means for dissipating heat rather than accumulating heat, which will more directly reduce the solar energy collected in the day-time.